This invention relates to electrical test equipment and more particularly to such apparatus which is adapted for testing axial lead devices while they are moving from an input bin to an output bin.
At the completion of the manufacturing process, axial lead electrical devices such as diodes and resistors must be tested to assure that their electrical characteristics fall within acceptable ranges. Automatic machines are known for testing and sorting such axial lead electronic components. An example of such a machine is the type 1620 magnetic axial lead sorter, manufactured by Daymarc Corporation of Waltham, Massachusetts. In this machine axial lead devices such as diodes are picked up from an input bin on the periphery of a magnetic carrier wheel. From the carrier wheel the diodes are transferred to an index table where the various electrical tests are performed. The index table is horizontal and moves in a step-wise fashion with a pause to allow the test to be performed at a fixed station. With this arrangement, the machine is capable of testing approximately 14,000 diodes per hour on a continuous basis. Although this machine is reliable and performs the electrical tests at a relatively high throughput rate, still higher throughput rates are desirable to keep up with ever greater production rates.
The Western Electric Company has also used magnetic carrier wheels to transport and test axial lead devices. U.S. Pat. Nos. 3,731,783 and 4,136,765 describe machines which use a magnetic carrier wheel for transport. U.S. Pat. Nos. 3,581,889 to Abraham et al. and 3,537,580 to Beroset et al. describe attempts to use a carrier wheel to both transport and test axial lead devices. The Abraham machine includes a stepping motor to drive the wheel in a step-wise manner. The devices carried on the wheel are tested one at a time at a fixed test station. This system involves a constant acceleration and deceleration of the wheel. The deceleration causes mechanical oscillation resulting in contact noise. Testing therefore must be delayed to allow decay of the oscillation. This decreases the available time for testing and certain tests cannot be performed at a single test station or they are performed at a single test station with diminished accuracy.
The Beroset device also uses a rotating carrier wheel. One or more test devices are mounted for movement in conjunction with the rotation of the wheel. The movement of the test device is controlled by a pawl that engages a ratchet wheel mounted on the carrier wheel, a bias spring and a pair of stops that define the angular limits of travel. The test device does not move radially; rather flexible contacts ride over the outer surface of the wheel during movement of the device. During a test period contact leads of the device rest on the leads of the product being tested without relative motion between them. While the Beroset system appears to avoid certain of the problems of the Abraham system, it also has problems. Each time the test device strikes a stop member, this collision generates a mechanical vibration. This electrical test must therefore wait for the vibration to dissipate. This results in a shortened test period with attendant disadvantages well known in the art.
It is therefore an object of this invention to provide an axial lead sorter/tester which has a two to three times higher throughput rate than previously known machines while maintaining a high degree of test accuracy.
Another object of this invention is to provide an axial lead sorter/tester which operates at an extremely high rate but is generally free of mechanical vibrations that can degrade the accuracy of the testing.
Yet another object of the invention is to provide a high speed test apparatus with a long test period.
It is a further object to provide such a machine which is highly reliable in its operation.
A still further object of this invention is an axial lead tester having a mechanically simple structure.
These and other objects and advantages of the invention will become apparent with reference to the following detailed description.